1. Field of the Invention
The present invention relates to contact lithographic masks having submicron features, and to a method for producing such masks. These tools are useful in the preparation of plating molds for fabricating metal microparts and are particularly useful for providing molds having lateral feature dimensions on the order of tenths to hundredths of microns while also having feature depth dimensions on the order of ten to hundred times those dimensions.
2. Description of Related Art
A variety of methods are presently known for making microparts. U.S. patent Ser. No. 5,256,360 to Li, teaches the use of a precisely controlled micro-electrode discharge machine (EDM) to make the micro-filter mold and suggests the use of laser-beam micro-machining, or electron-beam micro-machining, as suitable alternative processes. However, Li (""360), also teaches that molds made using conventional integrated circuits (IC) processing and lithographic processes in silicon tend to incorporate high internal strain, are prone to damage, are expensive to produce, and thus not economical to manufacture.
U.S. patent Ser. No. 5,501,893 to Laermer, et al. describes a lithographic technique for etching silicon, generally referred to as xe2x80x9canisotropic etching,xe2x80x9d where it is possible to achieve deeply-extending trenches while simultaneously providing side walls which are as nearly parallel and vertical as desired. In order to achieve these geometries it is necessary to allow etching to progress only on the bottom of the etched trench in the silicon substrate and not on the walls of the trench. In particular, Laermer (""893) teaches a two stage process for alternately etching an exposed silicon surface in a reactive ion plasma followed by coating the etched surfaces with a thin polymerized layer, wherein the polymer coating serves to protect the wall surfaces of the trench from action of the plasma since these surfaces are not directly face the incoming flux of plasma ions. However, the polymer layer applied to the xe2x80x9cfloorxe2x80x9d surface of the trench quickly breaks down in the presence of the ion bombardment since this surface directly faces the incoming ions. The polymer layer, therefore, forms a very effective etching xe2x80x9cstopxe2x80x9d on those edges or surfaces not directly in the path of the ion flux allowing for directional etching.
The process continues in this manner, alternating etching steps with coating steps, until the predetermined etching depth of the structures in the silicon substrate is reached.
Therefore, it is an object of the present invention to provide a process for fabricating highly accurate, three dimensional x-ray masking tools.
It is another object to provide an x-ray mask comprising a silicon substrate having a foil-like metal pattern embedded into the thickness of the substrate.
Yet another object of the invention is to provide an x-ray mask having an embedded metal pattern whose thickness is sufficient to attenuate virtually all x-ray radiation having an energy at or below 10 KeV which strikes the pattern in a direction parallel to the metal thickness.
It is another object of the invention to provide an x-ray mask wherein the embedded pattern comprises a plurality of structural elements exhibiting features having lateral dimensions of much less than 1 micron.
Still another object of the invention is to provide an x-ray mask wherein the features include both the structural elements comprising the pattern, and the separation distances between those elements.
Yet another object of the invention is to provide an embedded pattern having features exhibiting a height-to-width aspect ratio of greater than about 30-to-1.
Another object of the invention is to provide a robust x-ray mask tool which is capable of withstanding repeated handling and very long exposure to high-dose x-ray radiation.